1. Field of the Invention
The present invention relates, in general, to cooling tubes and is particularly, but not exclusively, applicable to cooling tubes used in conjunction with a plastic injection-molding machine to cool plastic parts, such as plastic parisons or preforms. More particularly, the present invention relates to a structural configuration of these cooling tubes, and also to methods of manufacturing and using such tubes, for example in the context of a manufacturing process for preforms made from polyethylenetetraphthlate (PET) or the like.
2. Summary of the Prior Art
In the injection molding art, it is known to use post mold cooling systems that operate simultaneously with the injection molding cycle. More specifically, while one injection cycle is taking place, the post mold cooling system, typically acting in a complementary fashion with a robotic part removal device, is operative on an earlier formed set of molded articles that have been removed from the mold at a point where they are still relatively hot, but sufficiently solid to allow limited handling.
Further, it is known to use fluid-cooled, cooling tubes for post-mold temperature conditioning of molded plastic parts, such as plastic parisons or preforms. Typically, such tubes are made from aluminum (or other materials having good thermal conductivity), and are formed by conventional machining methods from solid stock.
For example, each of U.S. Pat. Nos. 4,102,626 and 4,729,732 disclose a cooling tube formed with an external cooling channel machined in the outer surface of the tube body. A sleeve is then attached to the body to enclose the channel and provide an enclosed sealed path for the liquid coolant to circulate around the body.
WO 97/39874 shows a tempering mold that has circular cooling channels included in its body.
EP-A-0700770 discloses another cooling tube configuration for holding and cooling a preform that includes an elastically deformable holder with internal cooling passages, the holder operable between an open position and a holding position by exerting external force. Suggested embodiments include the internal cooling passages oriented in either a helical or longitudinal direction. No suggestion as to a method of manufacturing the holder or a specific construction (e.g. material) is given.
A problem with known cooling tubes is that they are expensive and are time-consuming to make and assemble. Further, the operational mass (i.e. including cooling water) of the cooling tube is of particular concern considering that a typical robot take-out system may include one or more sets of cooling tubes in an array, and therefore the cummulative mass supported by the robot quickly becomes a significant operating and/or design consideration (i.e. inertia or momentum considerations for the robot). Moreover, the robot typically operates to remove many tens of preforms in a single cycle (with present PET systems producing up to one hundred and forty-four preforms per injection cycle) so the energy expended by the robot and the technical specification of the robot are unfortunately relatively high. The provision and operation of a high specification robot therefore impose considerable financial cost penalties on an end user.
U.S. Pat. No. 5,870,921 discloses an extrusion die for use in producing aluminum alloy articles of extruded shapes or tube having a void with defined internal dimension.